correct gdm_display_store_foreach
gdm_display_store_foreach stops when the user returns TRUE. various callers erroneously return void or FALSE. this series makes gdm_display_store_foreach no longer rely on return value, and also fixes the callers.
gdm_display_store_foreach stops when the user returns TRUE. various callers erroneously return void or FALSE. this series makes gdm_display_store_foreach no longer rely on return value, and also fixes the callers.